Musnad Abu Ya'la al-Mawsili 148:75

Abu Khaythama narrated to us, Waki' narrated to us, Shu'bah narrated to us, from Hamzah al-Dabbi, who said: I heard Anas ibn Malik saying: When the Messenger of Allah (peace and blessings of Allah be upon him) would stop at a place, he would not depart until he had prayed Dhuhr. Muhammad ibn 'Amr said to him, "O Abu Hamzah, even if it were at midday?" He said, "Even if it were at midday."